Intermittent sorption cycles are conceptually very simple. In practice, however, an undesirable degree of complexity has heretofore been involved in their construction and/or operation. The very simplest cycles (two containers and a connecting conduit) require manual application and removal of heat. The more complex cycles, having heat supply and heat rejection means permanently located, have multiple components and control mechanisms which inflate their cost and reduce their reliability.
It is usual in intermittent sorption cycles to have the sorbent located in a single container which serves as both generator and absorber, plus separate components as the condenser and the evaporator. U.S. Pat. Nos. 4,183,227, 4,739,631, 4,742,868, 4,509,337 and 2,452,635 are examples of this.
It is desirable to have as much of the heat transfer required by the absorption cycle as possible brought about by thermosyphon (gravity heat pipe) operation. This avoids the need for pumped heat transfer loops. U.S. Pat. Nos. 2,293,556, 4,993,234, and 5,083,607 are examples of this.
In particular, it is desirable to cool the generator/absorber with a thermosyphon when it is in the absorb mode. However, rather than supplying a separate thermosyphon condenser (cold end), it is especially desirable to use the sorption cycle condenser also as the thermosyphon condenser. This is referred to as an integral thermosyphon. In addition to avoiding the need for a second condenser, it also avoids the need for a second refrigerant charge, as some of the cycle refrigerant is used as the thermosyphon working fluid. Prior art examples of an integral thermosyphon are found in U.S. Pat. Nos. 2,446,636 and 4,744,224.
The integral thermosyphon configuration has heretofore presented two problems: first, in order to turn the thermosyphon off and on at appropriate times, and also in order to isolate it from the remainder of the system when it is turned on and hence at high pressure, it has heretofore been necessary to have at least three refrigerant valves in the cycle. Secondly, when the thermosyphon is turned off, it is still partially full of liquid, and prior art systems cause a significant part of that liquid to be wastefully boiled away, resulting in a thermal loss. It would be much better to have the liquid removed from the thermosyphon by gravity drain (assisted by a very slight pressure boost).
What is needed, and one object of this invention, is a means for achieving the benefits of an integral thermosyphon in an intermittent sorption cycle while only requiring one or at most two valves for controlling the cycle, not the three or more traditionally required. A further need and objective is to provide a more efficient integral thermosyphon, i.e., one which when cut out need not evaporate the liquid from the TS evaporator, and which avoids thermal loss due to liquid drainback when cutout.